Implantable radioactive seeds for use in radiation therapy are described in U.S. Pat. No. 3,351,049. The seeds described therein comprise a tiny sealed capsule having an elongate cavity containing the radioisotope adsorbed onto a carrier body. The seeds are implanted directly into the diseased tissue. Because radioisotopes having short half-lives and emitting low energy X-rays, such as iodine-125, are used, the seeds can be left in the tissue indefinitely without excessive damage to surrounding healthy tissue or excessive radiation exposure to individuals in the patient's environment.
The use of absorbable sutures as carriers for iodine-125 seeds has greatly improved the ease and precision with which the seeds can be implanted into the tissue. Typically, each suture is loaded with up to twenty seeds, spaced one centimeter apart, and provided with a needle at one end. The object is to fill the body of the tumor, or tissue from which the tumor was excised, with radioactive seeds, set one centimeter equidistant from one another, to provide homogeneous radiation throughout the implanted volume. This is conveniently done by threading lengths of suture, loaded with seeds, through the tissue to be irradiated. Basic techniques for implanting the seed-carrying sutures into malignant tissue are described in "Surgical Radiation Therapy with Vicryl-.sup.125 I Absorbable Sutures", W. P. Scott, et al, Surgery, Gynecology and Obstetrics, Vol. 142, pp. 667-670, May, 1976.
One major problem associated with the use of radioactive seeds, particularly seeds contained within absorbable suture filament, involves packaging the seeds in a manner which allows for sterilization, yet minimizes radiation exposure to those individuals handling the seeds prior to and during implantation.
The most common method for shielding radioactivity is through the use of lead containers. Iodine-125 seeds are presently available commercially in lead storage/shipping containers (Medical Products Division of 3M, St. Paul, MN). The seeds are placed in glass vials inside the lead container. Before implantation into the tissue, the glass vials are removed from the lead container, the caps loosened, and the vials sterilized by steam or ethylene oxide. The seeds are then generally placed in a sterile shielding container of, for example, stainless steel, and transported to the operating room. Thus, for brief periods of time before and after sterilization and during the implantation procedure, the seeds are unshielded and those handling them are exposed to some radiation hazard.
Iodine-125 seeds in an absorbable suture carrier are not presently available commercially. However, methods for inserting the seeds into suture are known. (See for example, "A Method for Inserting I-125 Seeds into Absorbable Sutures for Permanent Implantation in Tissue", Bernice B. Palos et al., Int. J. Radiation Oncology Biol. Phys., Vol. 6, pp. 381-385, March, 1980. Radioactive seeds in this form pose an even greater risk of radiation exposure during implantation than individual seeds, because the seeds are physically attached to each other and must be handled in groups instead of individually.